1. Field of the Invention
The present invention relates to a wireless connection terminal and a roaming method for wirelessly communicating data by establishing a connection to an access point in a wireless network, such as a wireless LAN, and, in particular, to a roaming technology for use in a wireless network environment.
2. Description of the Related Art
In a wireless network environment, such as a wireless local area network (a wireless LAN), terminals are connected to the network via an access point installed in a public space or stores. Access points allow wireless connection terminals having a wireless communication function to connect thereto wirelessly. That is, data communication between the access point and the wireless connection terminals is performed by radio waves. However, the communication coverage area of one access point is limited. Accordingly, in general, in order to provide a wider wireless network environment, the communication coverage areas of a plurality of access points are disposed so as to be adjacent to each other (or partially overlapped).
In such a wide wireless network environment, a wireless connection terminal may move from the communication coverage area of an access point into the communication coverage area of another access point. For example, when a mobile information device is connected to a wireless LAN using a wireless module or when a laptop mobile personal computer is connected to a wireless LAN using a wireless communication adaptor, this situation occurs. In such a case, roaming is performed in which the wireless connection terminal selectively switches connection from the currently connected access point to another access point as the wireless connection terminal moves.
Roaming is a sequence in which the connection to the current access point is severed and, subsequently, connection to the next access point is established. To provide high-speed roaming, hopping information from the access point to which a station (a wireless connection terminal) is connected to another access point may be retrieved and downloaded. Thereafter, when the beacon quality of the access point to which the station is currently connected becomes less than or equal to a predetermined threshold value, an access point having the highest received signal strength indicator (RSSI) is selected for roaming on the basis of the downloaded information (refer to, for example, Japanese Unexamined Patent Application Publication No. 2001-94572 and, in particular, FIG. 1).
However, in the technology described in Japanese Unexamined Patent Application Publication No. 2001-94572, if the wireless connection terminal moves forward and backward across a threshold value boundary of the connected access point so that the RSSI of the connected access point unstably varies above and below the threshold value, roaming is performed every time the RSSI becomes lower than or equal to the threshold value. Thus, the communication is frequently disrupted.
In addition, in the technology described in Japanese Unexamined Patent Application Publication No. 2001-94572, roaming is performed when the RSSI of the access point is decreased to a value less than or equal to threshold value. Accordingly, if the threshold value is set to an extremely low value, the wireless connection tends to be unstable before and after roaming is performed. Furthermore, the communication is frequently disrupted due to the frequent roaming operations. Thus, the communication before and after roaming is performed tends to be incomplete.